In surgical procedures where significant blood loss may occur making it necessary to provide replacement blood to the patient, it has been found desirable to withdraw some of the patient""s blood and replace the volume of the blood withdrawn with a crystallized solution. This process, done just before the surgery, is generally known as hemodilution, and has developed based on recognition that the oxygen-carrying capacity of stored blood is greatly reduced and, further, that it contains metabolic products, which must be processed by the patient after transfusion. Hemodilution and use of the patient""s own blood that was withdrawn just before surgery to replace the blood lost during surgery has been found to provide better perfusion and reduced blood loss due to the dilution of the patient""s blood.
In prior hemodilution processes, the blood is withdrawn by draining it into a bag using only the patient""s venous pressure and the gravity head pressure naturally available by placing the bag below the patient. The flow rate attainable by this procedure is, however, very low, and the process requires too long, consuming expensive Operating Room time.
In accordance with the invention, the patient""s blood is withdrawn more quickly by applying a precisely-controlled vacuum. By this technique, the time required for withdrawal of a given volume of blood is reduced by more than one-half, when
compared to the prior art, gravity technique, and there is no measurable damage to the withdrawn blood.
In accordance with a method of the invention, a patient""s circulatory system is connected to a canister maintained at a vacuum controlled to be approximately xe2x88x92100 mm xc2x120 mm Hg. This level of vacuum allows the blood to be withdrawn very quickly and efficiently and avoids damage to the withdrawn blood or to the patient.
A preferred apparatus in accordance with the invention includes a tubing set for connecting the canister to a catheter access to the patient""s circulatory system, or to a needle. The tubing set includes a first tube section for connection to the catheter access or needle, a second tube section with a bag-piercing spike for connection to a source of anticoagulant, a third tube section for connection to the canister, and a stopcock joining the three tube sections for mixing anticoagulant with withdrawn blood and controlling the flows of the fluids in the three tubes. xe2x80x9cTubexe2x80x9d as used here is intended to refer to any sort of device for carrying fluids. In the preferred embodiment, the tubes are flexible tubes of physiologically compatible materials normally used in medical procedures.
The vacuum level, tubing sizes, e.g., the internal diameter (ID) and tubing length, are balanced so that the forces resulting from application of the vacuum to the patient""s circulatory system do not collapse the patient""s vein, but still provide pressure low enough to speed the withdrawal of venous blood. A vacuum that is too high and/or tubing and fittings that are too large would result in application of too much vacuum, and the resulting vein collapse would reduce or halt the flow. A vacuum that is too low, tubing and fitting that are too small in internal diameter, or tubing that is too long would not provide adequate reduced flow rate, extending blood collection time. Further, the relative sizes of the tubing and fittings connected to the patient and the tubing and fittings connected to the anticoagulant ensure that the proper amount of anticoagulant is mixed with the withdrawn blood and eliminate the possibility that anticoagulant will flow into the patient.